BIFUNCTIONAL CATALYST CONTAINING MULTIMETAL OXIDES

Abstract: This invention provides a bifunctional catalyst containing multimetal oxides, and a method for preparing the same. Said catalyst comprises a support of moulded mixture of silica and alumina in the weight ratio of 1:1.2-2.5, and upon said support is deposited 3-30% by weight of metal oxides based on the total weight of said catalyst. The metal elements of the metal oxides are at least two selected from transition metal of periodic 4 and lanthanides. Said metal oxides of the catalyst exist in the state of non-composite oxides.

Description: FIELD OF THE INVENTION This invention relates to a kind of catalyst, especially a catalyst with metal oxides as active components. BACKGROUND OF THE INVENTION Recently, catalytic techniques have been extensively used in many countries in the processes of chemical oxidation and reduction involved in petrochemical industry, chemical industry, environmental protection and treatment of industrial waste gas. However, the active, components in these catalysts are mainly nobel metals such as platinum, ruthenium, rhodium and palladium etc.. Therefore it becomes an important research subject in catalysis to find cheap materials with abundant reserve in place of the expensive and rare nobel metals (such as platinum). In seventies of this century, people began to make attempts to use composite oxides of rare earths as active components in catalysts etc.. The characters of these composite oxides, such as special electromagnetic properties, high temperature tolerance and good catalytic oxidative ability, have drawn extensive attention since long time ago. La 1-x Sr x CoO 3 , for example, was found to have very high activity for the oxidation of propane, methane and carbon monoxide (T. Nakamura, M. Misono et al., Nippon Kagaku, Kaishi 1980, 1679). It was also proposed in the early seventies to use composite oxides of rare earths in place of platinum in the catalyst for cleaning automobile exhaust gas [R.J.H. Voorhoeve, Science, 177, 353 (1972)]. Although, until now, many catalysts have been disclosed in which composite oxides were used as active components in place of nobel metals. Some problems such as the longterm stability and completeness of the structure of the composite oxides under the practical conditions still have not been solved. Therefore this kind of catalytic materials has not been well applied. Research on replacing nobel metals used as active components in catalysts with composite oxides is still in the test stage. No ideal results have been attained yet. In view of the above it is pointed at US-A-3,865,923. In this US-A an exhaust gas catalyst is disclosed consisting essentially of a first metal selected from copper, nickel and cobalt, a second metal selected from the rare earth metals and a third metal selected from manganese, vanadium, iron and chromium, all in an oxide form and deposited in a suitable catalyst support. The metal oxide deposit had a Perovskite type crystal structure. US-A-4,814,153 discloses a method of cleaning an exhaust gas containing nitrogen oxides, carbon monoxide, and an excess of molecular oxygen. This method comprises passing the exhaust gas together with ammonia over a first stage NO x catalyst consisting of (a) a titanium containing oxide and (b) a metal oxide selected from the oxides of vanadium, tungsten, molybdenum and tin and then passing the exhaust gas over a second stage catalyst consisting of (A) a catlytic oxide composed of a titanium containing oxide, (B) a catalytic oxide composed of at least one metal oxide selected from the oxides of copper, manganese and chromium and (C) a catalytic oxide composed of at least one metal oxide selected from the oxides of vanadium, tungsten, molybdenum, cerium and tin. SUMMARY OF THE INVENTION The object of the invention is to provide a catalyst containing multimetal oxides as active components which catalyst has good properties and can completely oxidize various organic compounds such as carbon monoxide, alkanes, alkenes and aromatic hydrocarbons etc., and decompose nitrogen oxides and sulfur oxides. Another object of the invention is to provide a method of preparing said catalyst and to provide products prepared by this method. The objects of the invention are realized by means of the following technical schemes. This invention provides a bifunctional catalyst containing metal oxides. The term "bifunctional" means that this kind of catalyst can be used not only as an oxidative catalyst but also a reductive one. This catalyst is prepared by depositing metal oxides, the amount of which is 3-30 wt.%, preferably 5-20 wt.%, more preferably 8-15 wt.% of the total weight of the catalyst, onto the outer and/or inner surface of the moulded support which is a mixture of silica and alumina in a weight ratio 1: 1.2-2.5. At least two of the metal elements, the number of which is usually 2-5, are selected from transition metals of period 4 of the periodic table of elements and lanthanides. Said metal oxides in the catalyst do not exist in the state of composite oxides. In particular, the selected metal oxides can be chromium oxide, manganese oxide, iron oxide, copper oxide, cobalt oxide, nickel oxide, zinc oxide, vanadium oxide, titanium oxide, lanthanum oxide and cerium oxide. The support can be in a shape of microspheric powder having a particle size of 60-100 µm or in a shape of a cylinder, ring, sphere, plate having a particle diameter of 3-5 mm or a honeycomb. The bifunctional catalyst containing multimetal oxides according to the present invention is prepared by the following method comprising the steps of: 1) mixing silica and alumina which are used as supports in a weight ratio of 1:1.2-2.5, moulding and calcining at 1000-1600°C for 2-8 hours in an oxidative atmosphere; 2) dissolving a nitrate or acetate of one element selected from transition metals of period 4 of the periodic table of elements and lanthanides to prepare. a 0.3-2 M solution and treating the calcined support by using the solution; 3) calcining the support treated in step 2) at 700-1200°C for 1-4 hours in a reductive atmosphere; 4) mixing nitrates or acetates of at lease two transition elements selected from the period 4 of the periodic table of elements and lanthanides to form a solution in which the total concentration of metal ions is 1-2.5 M, and adding a coordination agent selected from oxalic acid, amino acetic acid, 2-hydroxy-propanoic acid, succinic acid, hydroxy-butanedioic acid, tartaric acid, citric acid, o-phthalic acid, o-amino-benzoic acid and salicylaldoxime into the above solution in an amount of the added coordination agent being 1/4-3/4 of the total concentration of the metal ions to prepare the impregnant; 5) impregnating the support prepared by step 3), then drying and activating at 200-800°C for 1-4 hours to obtain said bifunctional catalyst containing multimetal oxides, The said transition metals of period 4 of the periodic table of elements and lanthanides are selected from chromium, manganese, iron, copper, cobalt, nickel, zinc, vanadium, titanium, lanthanum and cerium. In step 1), the support can be moulded into microspheric powders having a particle size of 60-100 µm or a cylinder-, ring-, spherical-, plate particles having a diameter of 3-5 mm or a honeycomb-shape. When preparing the impregnant, the mixed solution of manganese nitrate, cobalt nitrate and cerium nitrate can be. selected. The total concentration of the metal ions is 1-2.5 M and the molar ratio of various metal ions is 1:1:0.3-0.5. The mixed solution of copper nitrate, chromium nitrate and cerium nitrate can also be selected. The total concentration of the metal ions is 1-2.5 M and the molar ratio of various metal ions is 1:1:0.3-0.5. Further the mixed solution of copper nitrate and chromium nitrate can also be selected. The total concentration of metal ions is 1-2.5 M and the molar ratio of various metal ions is 1:1-2. The mixed solution of nickel nitrate, cobalt nitrate, cerium nitrate, chromium nitrate can also be selected. The total concentration of metal ions is 1-2.5 M and the molar ratio of various metals is 0.5:2.9:3:3.8. The mixed solution of iron nitrate, copper nitrate, cobalt nitrate, cerium nitrate and chromium nitrate can also be selected. The total concentration of metal ions is 1-2.5 M and the molar ratio of various metal ions is 1.3:2:2.7:3:4. The mixed solution of nickel nitrate, manganese nitrate, copper nitrate, cerium nitrate and chromium nitrate can also be selected. The total concentration of metal ions is 1-2.5 M and the molar ratio of various metal ions is 1:2-4.7:2.3:3:2-4.7. The mixed solution of nickel nitrate, cobalt nitrate, copper nitrate, cerium nitrate and chromium nitrate can also be selected. The total concentration of metal ions is 1-2.5 M. and the molar ratio of various metal ions is 1:2:2.3:3:4.7. The mixed solution of cobalt acetate, manganese acetate and lanthanum acetate can also be selected. The total concentration of metal ions is 1-2.5 M and the molar ratio of various metals is 1:1:0.04. The coordination agent added in the mixed solution is preferably citric acid. The said impregnation in step 5) can be operated at normal pressure or in vacuum. The number of metal elements in the mixed solution is generally 2.5. The detailed explanation of this invention will be as follows. The catalyst according to the present invention is obtained by depositing the oxides of active metals on a support consisting of silica and alumina. During the study of many years about the fundamentals of various composite metal oxides and metal oxides, we have realized that metal elements from period 4 of the periodic table of elements and lanthanides are the components that provide metal oxides with high activity. Besides, the special preparation procedures of this invention can make the active components distribute on the support firmly and uniformly, while not form bulk compounds with the support so that the long term stability and completeness of the prepared catalyst can be maintained. In this invention, when preparing the support, support materials made from silica and alumina are first calcined in an oxidative atmosphere, then it is treated in a solution of nitrate or acetate of a metal selected from period 4 of the periodic table of elements and lanthanides. After this treatment, it is again calcined under a reductive atmosphere. Here said treatment is a well-known method in the prior art, such as impregnation. The support can also be treated by a solution of nitrates or acetates of two or more metals. In the preparation method according to the present invention, a coordination agent such as citric acid is added into the mixed solution to make the solution stable and allow the active components to adhere on the support uniformly. According to the prior art, it is generally admitted that the safety can not be guaranteed if citric acid is used in the catalyst preparation technique. It is to be noted that the existing form of the active components in bifunctional catalyst containing multimetal oxides is a metal oxide, not the composite oxides such as ABO 2 , ABO 3 , AB 2 O 4 etc.. Said active components are distributed uniformly and adhere firmly in the form of metal oxides on the outer and/or inner surfaces of the support. So the prepared bifunctional catalyst is a kind of supported catalyst. In principle, composites of various metal oxides in any ratio and in agreement with the above demands can be used as active components. Best combinations should be selected according to different reaction requirements. The final product is obtained after the support is impregnated, dynamically dried by the technique known in the prior art, such as activation at 200-800°C for 1-4 hours. Further detailed explanation of this invention will be given in the following examples which do not limit this invention. All the agents in this invention are commercial products. BEST MODE FOR CARRYING OUT THE INVENTION Example 1 Combustion-assistant catalyst for the regeneration of fluidized catalytic cracking catalyst in petroleum refining 1) The microspheric powder support was prepared by spray. drying of the mixture of aluminum hydroxide and kaolin in a weight ratio SiO 2 : Al 2 O 3 = 1:1.8 into microspheric powders, calcining at 1400°C for 4 hours in an oxidative atmosphere, impregnating in the solution of cobalt nitrate (0.5M) and calcinating at 1000°C for another 2 hours in a reductive atmosphere. 2) Impregnant was prepared by mixing 400 ml of 2 M manganese nitrate, 400 ml of 2 M cobalt nitrate and 200 ml of 2 M cerium nitrate to form a solution in which the metal ions are in a molar ratio of 1:1:0.5, then adding 105 g of citric acid to the mixed solution. 3) The combustion-assistant catalyst was prepared by impregnating 100 g of microspheric powder in 60 ml of impregnant prepared as above for 0.5 hour at normal pressure, dynamically drying at 100°C and activating at 300°C for 2.5 hours. Example 2 Catalyst for cleaning the exhaust gas from gasoline engine 1) Al(OH) 3 and kaolin were mixed in the weight ratio of SiO 2 :Al 2 O 3 = 1:1.6. The mixture was extruded mechanically into strips, cut and shaped into the spheres. The support was prepared by repeating step 1) of example 1 except that cobalt nitrate solution was replaced with 0.5 M copper nitrate solution. 2) Impregnant solution was prepared by mixing 435 ml of 2 M copper nitrate, 435 ml of 2 M chromium nitrate and 130 ml of 2 M cerium nitrate to form a solution in which the metal ions were in a molar ratio of 1 : 1 : 0.3 and adding 105 g of citric acid to the mixed solution. 3) Catalyst for cleaning the exhaust gas from gasoline engine was prepared by impregnating 100 g of spherical support under vacuum in the impregnant (80ml) for 0.5 hr, drying at 100°C and then, activating at 300°C for 3 hours. Example 3 Catalyst for cleaning the exhaust gas from automobiles 40 ml of 2 M copper nitrate and 40 ml of 2 M chromium nitrate were mixed to form a solution in which the metal ions were in a molar ratio of 1 : 1. The impregnant was prepared by adding 8.5 g of citric acid to the mixed solution. 100 g of spherical support used in example 2 was impregnated in the prepared impregnant under vacuum for 0.4 hour, dried at 100°C and activated at 250°C for 4 hours. The catalyst which can be used for cleaning auto exhaust was obtained. Example 4 Catalyst for cleaning the exhaust gas from automobiles 15 ml of 2 M copper nitrate and 30 ml of 2 M chromium nitrate were mixed to form a solution in which the metal ions were in a molar ratio of 1:2. Impregnant was prepared by adding 5 g of citric acid to the mixed solution 50 g of spherical support used in example 2 was impregnated in the prepared impregnant under vacuum for 0.4 hour, dried at 100°C and activated at 320°C for 2.5 hours. The catalyst which can be used for cleaning auto exhaust gas was obtained. Example 5 Catalyst for cleaning the exhaust gas from automobiles. 4 ml of 2 M nickel nitrate, 23 ml of 2 M cobalt nitrate, 24ml of 2 M cerium nitrate and 30 ml of 2 M chromium nitrate were mixed to form a solution in which the metal ions were in a molar ratio of 0.5 : 2.9 : 3 : 3.8. Impregnant was prepared by adding 8 g of citric acid to the mixed solution. 100 g of spherical support used in example 2 was impregnated in the prepared impregnant under vacuum for 0.7 hour, dried at 100°C and activated at 350°C for 2 hours. The catalyst which can be used for cleaning auto exhaust gas was obtained. Example 6 Catalyst for cleaning the exhaust gas from automobiles 12 ml of 2 M iron nitrate, 19 ml of 2 M copper nitrate, 25 ml of 2 M cobalt nitrate, 28 ml of 2 M cerium nitrate and 37 ml of 2 M chromium nitrate were mixed to form a solution in which the metal ions were in a molar ratio of 1.3 : 2 : 2.7: 3 : 4. Impregnant was prepared by adding 13 g of citric acid to the mixed solution. 150 g of spherical support used in example 2 was impregnated in the prepared impregnant under vacuum for 0.7 hour, dried at 100°C and activated at 320°C for 2.5 hours. The catalyst which can be used for cleaning auto exhaust gas was obtained. Example 7 Catalyst for cleaning the exhaust gas from automobiles 12 ml of 2 M nickel nitrate, 25 ml of 2 M manganese nitrate, 28 ml of 2 M Copper nitrate, 37 ml of 2 M cerium nitrate and 58 ml of 2 M cobalt nitrate were mixed to form a solution in which the metal ions were in a molar ratio of 1 : 2 : 2.3 : 3 : 4.7. Impregnant was prepared by adding 16 g of citric acid to the mixed solution. 200 g of spherical support used in example 2 was impregnated in the impregnant under vacuum for 0.5 hour, dried at 100°C and activated at 280°C for 3.5 hours. The catalyst which can be used for cleaning auto exhaust gas was obtained. Example 8 Catalyst for cleaning the exhaust gas from automobiles 9 ml of 2 M nickel nitrate, 18 ml of 2 M cobalt nitrate, 21 ml of 2 M copper nitrate, 28 ml of 2 M cerium nitrate and 43 ml of 2 M manganese nitrate were mixed to form a solution in which the metal ions were in a molar ratio of 1 : 2 : 2.3 : 3 : 4.7 . Impregnant was prepared by adding 13 g of citric acid to the mixed solution. 150 g of spherical support used in example 2 was impregnated in the prepared impregnant under vacuum for 0.7 hour, dried at 100°C and activated at 250°C for 4 hours. The catalyst which can be used for cleaning auto exhaust gas was obtained. Example 9 Catalyst for cleaning the exhaust gas from automobiles 6 ml of 2 M nickel nitrate, 52 ml of 2 M cobalt nitrate, 14 ml of 2 M copper nitrate, 19 ml of 2 M cerium nitrate and 29 ml of 2 M chromium nitrate were mixed to form a solution in which the metal ions were in a molar ratio of 1 : 2 : 3 : 2.3 : 4.7. Impregnant was prepared by adding 9 g of citric acid to the mixed solution. 100 g of spherical support used in example 2 was impregnated in the prepared impregnant under vacuum for 0.5 hour, dried at 100°C and activated at 300°C for 2.5 hours. The catalyst which can be used for cleaning auto exhaust gas was obtained. Example 10 Combustion-assistant catalyst for catalyst regeneration in fluidized catalytic cracking in petroleum refining 25 ml of 2 M cobalt acetate, 25 ml of 2 M copper acetate, and 10 ml of 2 M lanthanum acetate were mixed to form a solution in which the metal ions were in a molar ratio of 1 : 1 : 0.04. Impregnant was prepared by adding 4 g of citric acid to the mixed solution. 100 g of spherical support used in example 1 was impregnated in the prepared impregnant at normal pressure for 0.5 hour, dynamically dried at 100°C and activated at 300°C for 2 hours. The combustion-assistant catalyst was obtained. INDUSTRIAL APPLICABILITY By adopting the above technical schemes the catalyst according to the present invention can completely oxidize various organic compounds such as CO, alkanes, alkenes and aromatic hydrocarbons under adequate conditions. So it is suitable for petroleum refining, - industrial waste gas treatment and .gas cleaning of special requirements. It can completely decompose the oxides of nitrogen and sulfur by treating the gases containing nitrogen oxide and sulfur oxide; promote the complete oxidation of CO and hydrocarbons and at the same time promote, the complete reduction of nitrogen oxides. The catalyst of this invention is especially suitable for cleaning the exhaust gas from gasoline engines. On the other hand, the catalyst of this invention can replace the catalyst containing nobel metals as active components, such as platinum, rhodium, ruthenium and palladium etc., and show more perfect catalytic performances than nobel metal catalysts. The following experimental examples will explain the industrial applicability. Experiment 1 5 g combustion-assistant catalyst prepared in example 1 was diluted 10 times and put into a small fixed fluidized bed. The composition of the reaction gas was 3% O 2 , 4% CO with N 2 remained. When the reaction was conducted at 300°C (catalyst bed temperature) and a space velocity of 5000 hr -1 (volume), CO conversion was 100%. CO conversion on the commercial Pt catalyst under the same conditions was less than 20% Experiment 2 30 g catalyst prepared in preparation example 2 was put into a Φ 30 m/m reactor. The composition of the reaction gas was 3% CO, 1500 ppm hydrocarbons, 500 ppm NO x , 1.5% O 2 . with N 2 remained. Under conditions of a space velocity (volume) 20000 hr -1 , reaction temperature (catalyst bed temperature) 250°C, CO conversion was higher than 95%, hydrocarbon conversion was higher than 70%, NOx conversion was higher than 70%. In Japan, conversions of CO, hydrocarbons and NO x of a promising catalyst for commercialization are considered to exceed 50% under the above reaction conditions. Experiment 3 30 g catalyst prepared in example 2 was put into a Φ 30 m/m reactor. The reaction gas was composed of 1% CO, 100 ppm hydrocarbons, 2000 ppm NO x , 0.5% O 2 with N 2 remained. Under conditions of a space velocity (volume) 20000 hr -1 and reaction temperature (catalyst bed temperature) 650°C, CO conversion was higher than 95%, hydrocarbon conversion was higher than 75%, the NO x conversion was 75%

Claims: A bifunctional catalyst containing multimetal oxides characterized in that 3-30 wt.% metal oxides based on the said catalyst is deposited as active components upon the outer and/or inner surface of a support of a moulded mixture of silica and alumina in the weight ratio of 1:1.2-2.5 calcined in an oxidative atmosphere; the metal elements of the metal oxides are at least two selected from transition metals of period 4 of the periodic table of elements and lanthanides; whereas said metal oxides of the catalyst do not exist in a state of composite oxides. A bifunctional catalyst containing multimetal oxides according to claim 1 characterized in that said metal oxides are selected from a group consisting of chromium oxide, manganese oxide, iron oxide, copper oxide, cobalt oxide, nickel oxide, zinc oxide, vanadium oxide, titanium oxide, lanthanum oxide and cerium oxide. A bifunctional catalyst containing multimetal oxides as according to claim 1 characterized in that said metal oxides are present in an amount of 5-20 wt.% based on the total catalyst. A bifunctional catalyst containing multimetal oxides according to claim 1 characterized in that said support has the shape of microspheric powder having a particle size of 60-100 µm, the shape of a cylinder, ring, plate having a particle diameter of 3-5 mm or a honeycomb. A bifunctional catalyst containing multimetal oxides according to claim 1 characterized in that the metal elements in said metal oxides as active components are 2-5 transition metals selected from the elements of period 4 of the periodic table of elements and lanthanides. A method for preparing a bifunctional catalyst containing multimetal oxides characterized in that it comprises the following steps: 1) mixing silica and alumina used as support in a weight ratio of 1:1.2-2.5, moulding and calcining at 1000°C - 1600°C for 2-8 hours in a oxidative atmosphere; 2) treating the above calcined support in a 0.3-2 M solution of a nitrate or acetate of a metal element, selected from transition metals of period 4 of the periodic table of elements and lanthanides; 3) calcining the support after treatment in step 2) at 700-1200°C for 1-4 hours in a reductive atmosphere; 4) mixing nitrates or acetates of at least two metal elements selected from transition metals in peruiod 4 of the periodic table of elements and lanthanides to form a solution in which the total concentration of metal ions is 1-2.5 M, and adding one coordination agent selected from oxalic acid, amino acetic acid, 2-hydroxy-propanoic acid, succinic acid, hydroxy-butanedioic acid, tartaric acid, citric acid, o-phthalic acid, o-aminobenzoic acid and salicylaldoxime into the mixed solution in an amount of the coordination agent being 1/4 - 3/4 of the concentration of the metal ions; 5) impregnating the support treateed in step 3) in the impregnant prepared in stel 4), then drying and activating at 200-800°C for 1-4 hours to obtain said bifunctional catalyst containing multimetal oxides in an amount of 3-30 wt.% based on the said catalyst, whereas said metal oxides do not exist in a state of composite oxides. A method according to claim 6 characterized in that said transition metal elements in period 4 of the periodic table of elements and lanthanides are selected from a group consisting of chromium, manganese, iron, copper, cobalt, nickel, zinc, vanadium, titanium, lanthanum and cerium. A method according to claim 6, characterized in that the said support is moulded into a shape of microspheric powders having a particle size of 60-100 µm or in the shape of a cylinder, ring, sphere, plate having a particle diameter of 3-5 mm or a honeycomb. A method according to claim 6 characterized in that the solution of nitrates or acetates of at least two elements selected from transition metals of period 4 of the periodic table of elements and lanthanides is a mixed solution of manganese nitrate, cobalt nitrate and cerium nitrate with a molar ratio of the metal ions being 1:1: 0.3-0.5 and the total concentration of the metal ions in this mixed solution being 1-2.5 M. A method according to claim 6 characterized in that the solution of nitratesor acetates of at least two elements selected from transition metals of period 4 of the periodic table of elements and lanthanides is a mixed solution of copper nitrate, chromium nitrate and cerium nitrate with a molar ratio of the metal ions being 1:1: 0.3-0.5 and the total concentration of the metal ions in this mixed solution being 1-2.5 M. A method according to claim 6 characterized in that the solution of nitrates or acetates of at least two elements selected from transition metals of period 4 of the periodic table of elements and lanthanides is a mixed solution of copper nitrate, and chromium nitrate with a molar ratio of the metal ions being 1:1-2 and the total concentration of the metal ions in this mixed solution being 1-2.5 M. A method according to claim 6 characterized in that the solution of nitrates or acetates of at least two elements selected from transition metals of period 4 of the periodic table of elements and lanthanides is a mixed solution of nickel nitrate, cobalt nitrate, cerium nitrate and chromium nitrate with a molar ratio of the metal ions being 0.5 : 2.9:3:3.8 and the total concentration of the metal ions in this mixed solution being 1-2.5 M. A method according to claim 6 characterized in that the solution of nitrates or acetates of at least two elements selected from transition metals of period 4 of the periodic table of elements and lanthanides is a mixed solution of iron nitrate, copper nitrate, cobalt nitrate, cerium nitrate and chromium nitrate with a molar ratio of the metal ions being 1.3 : 2 :2.7 : 3:4 and the total concentration of the metal ions in this mixed solution being 1-2.5 M. A method according to claim 6 characterized in that the solution of nitrates or acetates of at least two elements selected from transition metals of period 4 of the periodic table of elements and lanthanides is a mixed solution of nickel nitrate, manganese nitrate, copper nitrate, cerium nitrate and cobalt nitrate with a molar ratio of the metal ions being 1 : 2-4.7 : 2.3 : 3 : 2-4.7 and the total concentration of the metal ions in this mixed solution being 1-2.5 M. A method according to claim 6, characterized in that the solution of nitrates or acetates of at least two elements selected from transition metals of period 4 of the period table of elements and lanthanides is the mixed solution of nickel nitrate, cobalt nitrate, copper nitrate, cerium nitrate and chromium nitrate with a molar ratio of the metal ions being 1 : 2 : 2.3 : 3 : 4.7 and the total concentration of the metal ions in this mixed solution being 1-2.5 M. A method according to claim 6 characterized in that hte solution of nitrates or acetates of at least two elements selected from transition metals of period 4 of the periodic table of elements and lanthanides is a mixed solution of cobalt acetate, manganese acetate and lanthanum acetate with a molar ratio of the metal ions being 1:1: 0.04 and the total concentration of the metal ions in this mixed solution being 1-2.5 M. A method according to claim 6 characterized in that the said coordination agent is citric acid. A method according to claim 6 characterized in that the said impregnation in step 5) can be operated at normal pressure or vacuum. A method according to claim 6 characterized in that the said metal elements in their nitrate or acetate are 2-5 elements selected from transition metal elements of period 4 of the periodic table of elements and lanthanides.

Inventors: ZHOU HONGXING, ZHOU, HONGXING
Applicants: ZHOU HONGXING, ZHOU, HONGXING
Application year: 1994
Main classification: B01J23
IPC codes: B01J23, B01J21, B01D53, B01J37